In the past, leaf springs for vehicles have traditionally been fabricated from a series of superimposed steel leaves. Steel leaf springs are not only a relatively heavy construction but can be noisy, having a tendency to squeak, and are subject to corrosion. Recently, in order to decrease the overall weight of the vehicle, attempts have been made to utilize fiber reinforced resin materials as a substitute for steel leaf springs. In certain leaf springs of this type, the curved central section of the spring is molded from longitudinally extending fibrous material impregnated with the thermosetting resin and separate metal end sections are attached through mechanical connectors to the ends of the central section. This is a relatively expensive construction, for it is necessary to trim or machine the ends of the fiber reinforced resin leaf, drill connecting holes, and then assemble the metal brackets or connectors to the ends of the leaf. Furthermore, the trimming of the fibrous material results in exposed fiber ends which are susceptible to degradation from water and salt.
In other forms of fiber reinforced resin leaf springs, continuous strands of fibrous material impregnated with a thermosetting resin are wound around spaced bushings or pins in a loop configuration. After winding, the wound structure is placed in a mold with the parallel runs of the loop being brought together in flatwise contiguous relation and the resin is subsequently cured to provide an integral structure. In springs of this type, the fibrous strands extend continuously around the end sections and join the curved central section at neck regions and there is normally a small, transversely extending, V-shaped discontinuity bordering the opening in the end section, where the upper and lower runs are brought together in the neck region. In service, when a load is applied to the end portions of the spring, the spring may tend to delaminate, starting at the V-shaped discontinuity and progressing along the neutral axis. Further, torsional load applied to springs on turning of the vehicle, or torsional stress resulting from independent wheel suspension, can also have a tendency to delaminate the strands at the neutral axis in the neck region.
To prevent this delamination, it has been proposed to add clamps or other fasteners at the vulnerable neck region, but the addition of these fasteners normally requires holes, or other openings to be formed in the spring, which severs the longitudinally extending reinforcing strands and correspondingly reduces the physical characteristics of the spring.